Arc fault detection using frequency hopping techniques

ABSTRACT

An arc fault detection system samples a high frequency signal on a power line sequentially at different frequency regions according to a frequency hopping sequence, which is repeated a number of times over a predefined period. The different frequency regions include at least one region with a carrier for power line communication on the power line and at least one region without a carrier for power line communication on the power line. The system obtains energy measurements for each frequency region based on the sampled signals, computes an energy level for each frequency region based on the measurements for each region, and assigns a binary value to each region according to the corresponding energy level. The binary value represents a presence or absence of signal content in the frequency region. The system determines a presence or absence of an arc fault based on the binary values for the frequency regions.

PRIORITY

The present U.S. patent application is a continuation of U.S. patentapplication Ser. No. 15/985,823, filed May 22, 2018, and claims priorityunder 35 U.S.C. § 120. The disclosure of the above priority applicationis incorporated herein, in its entirety, by reference.

FIELD

The present disclosure is related to a method and system for improvingarc fault detection, and more particularly, to a method and system forimproving interoperability of arc fault detection and power linecommunications (PLC) in a branch circuit.

BACKGROUND

Power line communication (PLC) devices can be used in buildings, such asa residential home (e.g., house, condominium, apartment, etc.), toenable data communications across a power system infrastructure, such aspower lines of a branch circuit(s). PLC devices conduct communicationsin the high frequency ranges, such as for example in the unregulatedrange from 2 MHz to 30 MHz and to as high as 86 MHz (see, e.g., HomePlugAvx and HomePlug GreenPhy). Power line communication protocol used byPLC devices can include, for example, IEEE 1901, IEEE P1901.2, HomePlugGP/AV/AV2/1.0, G.hn, or G.hnem. When PLC devices are employed in abuilding or other structure along with an arc fault circuit interrupter(AFCI) device, the presence of PLC signals, particularly the highfrequency content of their carrier signals may be inadvertentlyinterpreted by the AFCI device as arc fault signals, and thus, mayresult in nuisance trips by the AFCI device. Accordingly, PLC signalsand other high frequency noises may interfere with arc fault detectionat the high frequency ranges, e.g., frequency ranges greater than orequal to 1 MHz.

One method to detect the presence of power line carriers is based on theReceiver Signal Strength Indicator (RSSI) of high frequency content ofpower line carriers. However, the RSSI method does not appear to berobust due to the fact that RSSI does not contain frequency information,and therefore, any arc fault signal could look like a PLC signal orvice-a-versa from the signal strength point of view. This RSSI methodthus can not be used to detect for an AF signal.

Another detection method involves selecting a frequency region (e.g.,region, band, etc.) that corresponds to one of the notch bands of thepower line carriers. The notch bands represent narrow frequency regionsthat are not enabled or used by the PLC device to conduct communication.However, such a detection method allows only a small window, e.g., anarrow frequency region, for the arcing signals to be detected.Furthermore, such a frequency region might be used by radio stations(e.g., amateur radio) or correspond to a network impedance(resonance/anti-resonance) point which could cause substantialsensitivity issues.

SUMMARY

To address these and other shortcomings, an arc fault detection methodand system are provided, which monitor and analyze high frequencysignals on a power line of a circuit to detect for an arc fault event.The arc fault detection method and system sequentially sample a highfrequency signal from the power line at different frequency regionsaccording to a frequency hopping sequence, which is performed multipletimes to obtain a plurality of sampled signals for each frequency regionin the sequence over a predefined period of time, e.g., a half-cycle ofa base frequency. The frequency hopping sequence has one or morefrequency regions that include a carrier of power line communication orknown high frequency noise, and one or more frequency regions thatexclude a carrier of power line communication or known high frequencynoise. The arc fault detection method and system measure and evaluatethe energy of the sampled signals for each frequency region to determinea presence or absence of signal content in each frequency region of thesequence. Given the wide-band nature of arc fault signals, an arc faultcan thus be detected based on the presence or absence of signal contentacross the different frequency regions within the predefined timeperiod.

Accordingly, arc fault detection can be performed in the high frequencyrange (e.g., 1 MHz and greater, 1 MHz up to 40 MHz, with the currentdesign, etc.), which is subject to less load noise than lower frequencyranges (e.g., such as noise from vacuum cleaners, ballasts, switchingmode power supplies which range from 20 kHz to 100 kHz, etc.). The arcfault detection method and system can sample and evaluate high frequencysignals on the power line to detect for an arc fault signal, even whenhigh frequency noise may be injected onto the power line from power linecommunication or other known high frequency noise injecting activities.Furthermore, signals are sampled for each frequency region atspaced-apart time intervals within the predefined time period to providea more reliable assessment of the energy in each frequency region. Bysampling signals using a combination of frequency regions which includeor exclude known noise carriers, it is also possible to betterdiscriminate such noise (e.g., PLC signals) from arc fault frequencysignals to reduce nuisance detection and tripping.

In accordance with an embodiment, an arc fault detection method andsystem are provided to detect an arc fault on a power line. The arcfault detection method and system sample a high frequency signal on apower line sequentially at different frequency regions according to afrequency hopping sequence over a predefined time period. The samplingsequence is performed a number of times over a predefined time period.The different frequency regions include at least one frequency regionthat includes few carriers for power line communication on the powerline and at least one frequency region that does not contain anycarriers for power line communication on the power line. The arc faultdetection method and system further obtain a plurality of energymeasurements for each frequency region in the frequency hopping sequencebased on the sampled high frequency signals; compute an energy level foreach frequency region of the frequency-hopping sequence based on theplurality of energy measurements for each frequency region; and assign abinary value to each frequency region in the frequency hopping sequenceaccording to the energy level corresponding to the frequency region. Thebinary value represents a presence or absence of signal content in thefrequency region. The arc fault detection method and system candetermine a presence or absence of an arc fault event based on thebinary values for the frequency regions of the frequency hoppingsequence. When an arc fault event is detected, power can be interruptedon the power line.

The predefined time period can be a half-cycle of a base frequency. Thefrequency of each frequency region can sequentially increase or decrease(or not) in the frequency hopping sequence.

To obtain an energy measurement, the arc fault detection method andsystem can, for each iteration of the frequency hopping sequence,generate an energy envelope or receiver signal strength indicator (RSSI)sample, e.g., an RSSI voltage sample, for each frequency region in thefrequency hopping sequence based on the sampled high frequency signals.To compute an energy level, the arc fault detection method and systemcan, for each frequency region, auto-correlate the plurality of energyenvelopes or RSSI voltage samples of the frequency region to obtain apeak energy value as the energy level, or sum squared RSSI samples(e.g., RSSI voltage samples) of the frequency region to obtain a summedenergy value as the energy level.

The frequency hopping sequence can include a sequence of M frequencyregions (or steps), and the frequency hopping sequence is performed Ntimes during one half-cycle. The arc fault detection method and systemcan compute the energy level E for each of the M frequency regionsduring one half-cycle by determining the peak of autocorrelation of theN samples or in a similar way by summing the square of N samples foreach frequency step (M):E _(m)=max(ACR_(m))=Σ_(i=n) ^(N) S _(mi) ²,where: m is the order frequency region between 1 to a maximum M in thefrequency hopping sequence, n is a number from 1 to a maximum N that thefrequency hopping sequence is performed, and S is an energy measurementsample at a frequency step of a frequency hopping sequence.

To sample a high frequency signal, the arc fault detection method andsystem can, for each frequency region in the frequency hopping sequence,down convert the high frequency signal associated with the frequencyregion, apply a low pass filter to the down converted signal, andgenerate an energy envelope or RSSI sample for the filtered signal.

The arc fault detection method and system can determine a presence orabsence of an arc fault event when the binary values satisfy apredefined condition.

The arc fault detection system can include an analog front end, a memoryand a processor. The analog front end can include a mixer configured tosequentially demodulate the high frequency signal at different frequencyregions according to the frequency hopping sequence using a localoscillator or phase locked loop. The high frequency signal isdemodulated by the mixer to a baseband signal. The analog front end canfurther include one or more band pass filters to filter the highfrequency signal or the demodulated baseband signal or both to narrowthe band to a region of interest.

DESCRIPTION OF THE FIGURES

The description of the various example embodiments is explained inconjunction with the appended drawings.

FIG. 1 illustrates a block diagram of a circuit breaker with an arcfault detection system which samples high frequency signals on a powerline using frequency hopping sequence in accordance with an exampleembodiment of the present disclosure.

FIG. 2 illustrates a block diagram of components of the arc faultdetection system, such as in the circuit breaker of FIG. 1, to samplehigh frequency signals on the power line using a frequency hoppingsequence which sweeps a number of times over a predefined time periodthrough a mixing configuration with a voltage controlled localoscillator in accordance with an example embodiment of the presentdisclosure.

FIG. 3 illustrates a block diagram of components of the arc faultdetection system, such as in the circuit breaker of FIG. 1, to samplehigh frequency signals on the power line using a frequency hoppingsequence which sweeps a number of times over a predefined time periodthrough a mixing configuration with a phase locked loop in accordancewith an example embodiment of the present disclosure.

FIG. 4 illustrates a functional block diagram of signal processingoperations of the arc fault detection system, such as in the circuitbreaker of FIG. 1, to detect an arc fault event, which in turn initiatesa power interruption operation in accordance with an example embodimentof the present disclosure.

FIG. 5 illustrates a flow diagram of an example process implemented bythe arc fault detection system, such as in the circuit breaker of FIG.1, by which an arc fault signal is detected from high frequency signalsmonitored on a power line in accordance with an example embodiment ofthe present disclosure.

FIG. 6 illustrates a graph of magnitude versus frequency of an examplepower line communication (PLC) signal showing frequency regions whichinclude and exclude PLC carrier regions.

FIG. 7 illustrates a graph of impedance versus frequency of a powerline, showing frequency selection criteria based on the networkimpedance in accordance with an example embodiment of the presentdisclosure.

FIG. 8 illustrates a graph of frequency versus time of an examplefrequency hopping sequence of frequency regions for sampling highfrequency signals on a power line in accordance with an exampleembodiment of the present disclosure.

FIG. 9 illustrates a graph of frequency versus time of an examplefrequency hopping sequence of frequency regions for sampling highfrequency signals on a power line in accordance with another exampleembodiment of the present disclosure.

FIG. 10 illustrates energy measurement samples, such as for example RSSIsamples, for a M-region frequency-hopping sequence, which is implementedN-times over a predefined time period, such as a half-cycle of a basefrequency, in accordance with another example embodiment of the presentdisclosure.

FIG. 11 illustrates an example M×N matrix of the energy measurementsamples, such as in FIG. 10, which is generated and used to calculate anenergy level of each region in the frequency-hopping sequence over apredefined time period in accordance with another example embodiment ofthe present disclosure.

FIG. 12 illustrates a voting strategy for determining a presence orabsence of an arc fault event according to the calculated energy levelsfor each region of the frequency hopping sequence in accordance withanother example embodiment of the present disclosure.

DISCUSSION OF EXAMPLE EMBODIMENTS

FIG. 1 illustrates a block diagram of an example circuit breaker 100with an arc fault detection system for monitoring a high frequencysignal(s) on an AC power line 10 (e.g., 50/60 Hz power line) of aprotected circuit 20. The circuit breaker 100 includes a controller 110,an analog front end (AFE) 120 to receive signals from a high frequency(HF) sensor 180, a memory 130, a communication interface 140 tocommunicate with remote or other devices or systems over acommunication/transmitting medium, a user interface 150, a power supply160 to power the components of the circuit breaker 100, and a tripmechanism 170 to interrupt power on the power line 10 upstream of theprotected circuit 20. The user interface 150 can include an ON/OFFswitch 152 (e.g., a handle), a push-to-test (PTT) button to test thecircuit breaker, and one or more LEDs or other indicators for indicatinga status of the circuit breaker (e.g., ON, OFF, RESET, TRIPPED, etc.) orother circuit breaker information. The HF sensor 180 can be a highfrequency current sensor such as a radio frequency (RF) sensor orreceiver, Rogowski coil or other sensor to measure high frequencysignals on the power line.

In the circuit breaker 100, the controller 110, the AFE 120 and thememory 130 can operate together to provide an arc fault detectionsystem, which is configured to detect arc fault signals in the highfrequency range on the power line 10. The AFE 120 is configured toreceive or monitor high frequency signals at desired high frequencyregion(s) from the HF current sensor 180, and can include bandpassfilters and other components for filtering and conditioning signals.

As will be described in further detail herein, the AFE 120 is furtherconfigured, among other things, to sample high frequency signals on thepower line 10 sequentially at different frequency regions according to afrequency hopping sequence, and to down convert the sampled signals forsignal processing for each frequency region in the frequency hoppingsequence. The different frequency regions in the frequency hoppingsequence can include one or more frequency regions that include acarrier for power line communication on the power line 10 and/or knownhigh frequency noise, and one or more frequency regions that exclude acarrier for power line communication on the power line 10 and/or knownhigh frequency noise. The AFE 120 is configured to implement a frequencyhopping sequence of M-frequency regions which is performed N-number oftimes, where M is the number of frequency regions in the frequencyhopping sequence and N is the number of times the frequency hoppingsequence is performed within a predefined time period (e.g., ahalf-cycle of a base frequency, a full-cycle of a base frequency or anygreater number of half-cycles).

The controller 110 is configured to process and measure energy on thesampled high frequency signals at the different frequency regions (ofthe frequency hopping sequence) received from the AFE 120, and to detectfor a presence or absence of an arc fault event based on an energy levelof each region. For example, the controller 110 is configured to obtaina plurality of energy measurements (e.g., energy envelope or RSSIsample) of the sampled signals for each frequency region in thefrequency hopping sequence based on the sampled high frequency signals,and to compute an energy level for each frequency region of thefrequency-hopping sequence based on the plurality of energy measurementsfor each frequency region. The controller 110 is further configured toassign a binary value to each frequency region in the frequency hoppingsequence according to the energy level corresponding to the particularfrequency region. The binary value represents a presence or absence ofsignal content in the frequency region. The controller 110 is alsoconfigured to determine a presence or absence of an arc fault based onthe binary values for the frequency regions of the frequency-hoppingsequence and to cause or initiate a trip operation, which interruptspower on the power line 10 via the trip mechanism 170 when an arc faultevent or other events are detected.

Furthermore, the controller 110 is also configured to control theoperations of the circuit breaker 100 including communication via thecommunication interface 140 (e.g., to receive or transmit commands,status information/reports, or updates), to perform operations based onactions taken through the user interface 150 by a user, to output astatus of the circuit breaker 100 such as via the LED 156, and toperform other operations of the circuit breaker 100 related to arc faultdetection and power interruption. Although various signal processingoperations for arc detection is described as being performed by thecontroller 110, one or more of the operations can instead be implementedin a separate processor/processing device in communication with thecontroller 110, such as in an ASIC or FPGA which can communicate withthe AFE 120 or include the components of the AFE 120.

The memory 130 can store computer executable code or programs orsoftware, which when executed by the controller 110, controls theoperations of the circuit breaker 100 and its components including thearc fault detection operations and other circuit breaker operations suchas circuit interruption. The memory 130 can also store other data usedby the circuit breaker 100 or components thereof to perform theoperations described herein. The other data can include but is notlimited to one or more selectable frequency hopping sequences offrequency regions, one or more selectable predefined time periods, oneor more predefined conditions (e.g., energy measurement thresholds foreach or all frequency regions, and frequency region/energy levelpatterns or thresholds for the frequency regions and other predefinedconditions to determine an energy level for each frequency region and apresence or absence of an arc fault event), circuit breaker operatingparameters, and other circuit breaker data. Some of the data in thememory 130 can also be maintained or stored instead in a memory of thecontroller 110 or other components of the circuit breaker 100 dependingon the system design.

FIG. 2 illustrates a block diagram of example components of the AFE 120and the controller 110 of the arc fault detection system, such as in thecircuit breaker 100 of FIG. 1, to sample high frequency signals on thepower line 10 using a frequency hopping sequence which is performed anumber of times over a predefined time period. As shown in FIG. 2, theAFE 120 can include a band pass filter 202, a mixer 210, a low passfilter 212, an RSSI/LogAmp 214 and a local oscillator (LO) generator250. The controller 110 can include one or more processors 220, ananalog-to-digital converter (ADC) 230, a digital-to-analog converter(DAC) 240 and a memory 250 for storing processed data and new data to beprocessed along with other configuration data (e.g., parameters,thresholds, etc.) used to implement the arc fault detection methoddescribed herein.

The band pass filter 202 receives signals, e.g., high frequency signals,which are detected on the power line 10 by the HF sensor 180, andfilters the signals to a narrower band. In this example, the band passfilter can allow signals which are between the frequency ranges of about1 to 40 MHz to pass. The mixer 210 (e.g., a heterodyne device)down-converts high frequency signals (e.g., between 1 MHz and 40 MHz) ata desired frequency region to baseband according to the signalsgenerated by and received from the LO generator 250 (e.g., a voltagecontrolled oscillator (VCO) generator). The LO (local oscillator)generator 250, which is controlled by the controller 110, is configuredto generate LO signals for different frequency regions of a frequencyhopping sequence. The LO generator 250 cycles (or sweeps) through thefrequency hopping sequence of the different frequency regions ofinterest (e.g., frequency steps 1, 2, 3, 4 and 5). As the LO generator250 cycles through each frequency region in the frequency hoppingsequence, the mixer 210 sequentially outputs two signals, adown-converted signal to the local oscillator frequency and anup-converted signal a multiple of the local oscillator frequency.

These signals are filtered by the low pass filter 212 to allow only thedown-converted signals which represent the baseband signals (e.g., 10kHz up to 150 kHz) of interest received from the band pass filter 202 atthe different frequency regions according to the frequency hoppingsequence.

The RSSI or LogAmp 214 can be a logarithmic amplifier or an RF amplifierwith fast automatic gain control (AGC) which outputs a representativeenergy envelope of the signal (e.g., an RF signal) that is received fromthe low pass filter 212. The energy envelope, which is sometimesreferred to as the receiver signal strength indicator (RSSI) or RSSIsample or signal, reflects an energy measurement of the monitoredsignals on the power line 10 at a particular frequency region of thefrequency hopping sequence.

The ADC 230 converts the RSSI sample (e.g., in Volts) to a digitalrepresentation (e.g., 16-bits, etc.) for subsequent processing by theprocessor 220 of the controller 110. The controller 110 can be amicrocontroller with built-in successive approximation ADCs havingdifferent resolutions (e.g., 6 to 16-bits) and configurable samplingrates (e.g., 10 to 1 M samples per second). The digital output of theADC 230 is stored in the memory 250, and processed by the processor 220to detect for a presence or absence of an arc fault according to the arcfault detection methods described herein. The processor 220 controls thesampling of signals from one frequency region to the next frequencyregion in the frequency hopping sequence, via the DAC 240 and the LOgenerator 250. The sampling rate can be determined based on the numberof frequency steps (e.g., M steps or 5 in this example) and the numberof repetitions (e.g., N repetitions of the frequency hopping sequence)within a predefined time period (e.g., a half-cycle period). In thisway, the processor 220 can evaluate N energy measurements for each ofthe M frequency regions in order to detect for a presence or absence ofan arc fault event.

FIG. 3 illustrates a block diagram of components of the arc faultdetection system, such as in the circuit breaker FIG. 1, to samplesignals on the power line using a frequency hopping sequence which isimplemented a number of times over a predefined time period inaccordance with another example embodiment of the present disclosure. Inthis alternative example, the arc fault detection system generallyincludes the same components as that in the example of FIG. 2, exceptthat, in AFE 120A, a phase locked loop (PLL) 350 is used to implementthe mixing operations for the different frequency regions according tothe frequency hopping sequence.

FIG. 4 illustrates a functional block diagram of signal processingoperations performed by the different modules/components of the arcfault detection system, such as in the circuit breaker 100 of FIG. 1, todetect an arc fault event, in accordance with an example embodiment ofthe present disclosure. In this example, a plurality of energymeasurements for each of the frequency regions of the frequency hoppingsequence is taken over a predefined period, e.g., a half-cycle period.

At block 400, zero-crossing is detected to begin arc fault detectionsignal processing operations for a half-cycle period. At block 402, ahigh frequency signal sensed by the HF sensor 180 (e.g., a HF currentsensor) is filtered by a band pass filter to a narrower high frequencyband. At block 410, the filtered signal is mixed with an LO signal froma local oscillator generator to down-convert the filtered signals at aparticular frequency region (from a plurality of different frequencyregions of a frequency hopping sequence) to a baseband. The frequencyregion of the signal to be demodulated is controlled and changed by thelocal oscillator generator at block 450 from one frequency region to thenext region in a step by step manner over time according to thefrequency hopping sequence (at block 460). Alternatively, the frequencyhopping sequence of operations can be implemented using a PLL (e.g.,FIG. 3).

At block 412, the down-converted and up-converted signals are filteredby a low pass filter to allow a narrow band of the down-convertedbaseband signal. At block 414, a gain is applied to the filtered signalto produce an energy envelope, which reflects a measurement of thesignal strength of the high frequency signal (e.g., RF signal) at thesampled frequency region. A logarithmic amplifier or a RF amplifier withfast automatic gain control (AGC) can be used to produce the energyenvelope, e.g., a sample of the RSSI voltage or the like. At block 430,the energy envelope is converted using an ADC from an analog signal to adigital signal, e.g., a digital word (e.g., 6 to 16-bits).

At block 440, a matrix of energy measurements is formed from M frequencyregions in the frequency hopping sequence, and N sweeps of the sequenceof frequency regions within the half-cycle of the base frequency (e.g.,power line frequency 50/60 Hz). The matrix can be an M×N matrix of RSSIsamples, which form an RSSI space for the half-cycle. For example, a setof M vectors contains all of the N samples of the energy measurements,e.g., RSSI samples, acquired during the predefined period of ahalf-cycle. An example of a set of vectors for the frequency regions isshown in FIG. 11 (e.g., S₁₁ . . . S_(1N), . . . S_(M1) . . . S_(MN),where M is the number of frequency regions in the frequency hoppingsequence, and N is the number of repetitions of the sequence).

At block 442, the energy level of N samples is computed for eachfrequency region within the half-cycle. This calculation is, forexample, computed for each frequency region by performing N summationsof squares of each energy measurement sample (e.g., RSSI voltagesample), or computing the peak of auto-correlation of N RSSI samples.The computation is performed on each of the M vectors in the RSSI spacefor each frequency region in the frequency hopping sequence. An exampleof the energy level computation for each frequency region is shown inFIG. 11, which is discussed further below.

At block 460, the sampling of signals, which are monitored on a powerline, is controlled on a sequential step-by-step basis from onefrequency region to the next frequency region of the frequency hoppingsequence over time, via the LO signal generated by generated by thelocal oscillator generator (at block 450). The sequence of frequencyregions are repeated N times, for example, within the predefined periodof a half-cycle. Accordingly, over the half-cycle, for each frequencyregion, the ADC operation at block 430 samples the RSSI, e.g., an RSSIvoltage sample, at the output of the RSSI log amplifier (at block 414)and stores the digital sample S in memory (e.g., S_(M×N)) for furtherprocessing at blocks 440 and 442 as previously discussed above. Themodule implementing (Frequency Steps) block 460 can provide for thesynchronization of the operations of the local oscillator generator (atblock 450) in implementing and repeating the frequency hopping sequence,and of the energy calculations from the sample vectors (at block 442).

At block 470, an energy threshold is applied to the computed energylevel for each M frequency region, which is then converted to a binaryvalue reflecting a presence or absence of high frequency content in thefrequency region based on the comparison. For example, each of the Mfrequency regions (in the frequency hopping sequence) is assigned abinary value, e.g., 0 or 1, based on whether enough RSSI energy waspresent in the frequency region during the predefined period of ahalf-cycle. Because all of the energy samples for each frequency regionare time dependent, the accumulative energy for each frequency region iscompared against an energy threshold which can for example be determinedempirically by experimentation in a laboratory environment. Inoperation, a frequency region can for example be assigned a value of 1if the threshold condition is satisfied, and a value of 0 if thethreshold condition is not satisfied (or vice-a-versa). Because arcinggenerates wide band RF signals and lasts for the most part of thehalf-cycle, the overall energy can be measured in such a manner for eachfrequency region.

At block 480, the energy levels for all of the frequency regions areevaluated based on a predefined condition(s) (e.g., a voting strategy,predefined thresholds, frequency region/energy level patterns, etc.).The predefined conditions can be defined by the number and nature of thefrequency regions having and/or not having high frequency content withinthe predefined time period. In another example, an arc fault event isdetected if a total number of frequency regions identified as havinghigh frequency content satisfies a number threshold, or acombination/pattern of certain regions with and/or without noisecarriers are found to have high frequency content. As previouslydiscussed, the frequency regions can have one or more regions thatinclude a carrier of power line communication or other known noise, andone or more regions that exclude a carrier of power line communicationor other known noise. A further example of a predefined condition isprovided in the voting strategy example of FIG. 12, which is discussedfurther below.

In the event that the predefined condition is satisfied, an arc faultevent is detected on the power line, and accordingly, power can beinterrupted on the power line via a trip mechanism to provide forcircuit protection.

FIG. 5 illustrates a flow diagram of an example process 500 implementedby the arc fault detection system, such as in the circuit breaker 100 ofFIG. 1, by which an arc fault signal is detected from signals monitoredon a power line in accordance with an example embodiment of the presentdisclosure. For the purpose of explanation, the process 500 will bedescribed with reference to the components of the circuit breaker 100 ofFIG. 1, such as the controller 110 and AFE 120.

At step 502, the AFE 120 samples a high frequency signal on a power linesequentially at different frequency regions according to a frequencyhopping sequence. The different frequency regions include at least onefrequency region that includes a carrier for power line communication(or other known noise) on the power line and at least one frequencyregion that excludes a carrier for power line communication (or otherknown noise) on the power line. The AFE 120 can also perform filteringand conditioning on the sampled signals. At step 504, the AFE 120repeats the sampling of high frequency signals on the power lineaccording to the frequency hopping sequence a number of times. Forexample, the sequence is repeated in total N times to generate N signalsamples for each of the M frequency regions in the sequence over apredefined time period. As previously discussed, the controller 110 cancontrol signal sampling according to the frequency hopping sequence overtime via an LO generator or PLL.

At step 506, the AFE 120 obtains a plurality of energy measurements(e.g., RSSI voltage samples) of the sampled high frequency signals foreach frequency region in the frequency hopping sequence based on thesampled high frequency signals. The energy measurements can be convertedto a digital form for processing by the controller 110. At step 508, thecontroller 110 computes an energy level for each frequency region of thefrequency-hopping sequence based on the plurality of energy measurementsfor each frequency region. For example, the energy level for eachfrequency region can be determined by performing N summations of squaresof the RSSI samples (e.g., RSSI voltage samples) for the frequencyregion, or by computing the peak of auto-correlation of N RSSI samples.

At step 510, the controller 110 assigns a binary value to each frequencyregion in the frequency hopping sequence according to the energy levelcorresponding to each frequency region. The binary value represents apresence or absence of signal content in the frequency region over thepredefined period of time.

At step 512, the controller 110 determines a presence or absence of anarc fault event based on the binary values for the frequency regions ofthe frequency-hopping sequence. For example, the energy levels areevaluated in relations to predefined conditions (e.g., predefinedthresholds, frequency region/energy level patterns, etc.). An arc faultevent is detected when the energy levels for the frequency regions ofthe frequency hopping sequence satisfy the predefined condition.

At step 514, when an arc fault event is detected, the controller 110causes the interruption of power on the power line, e.g., by tripping atrip mechanism or other power interruption device.

FIG. 6 illustrates a graph 600 of magnitude versus frequency of examplepower line communication (PLC) signals showing frequency regions whichinclude and exclude PLC carrier regions. As shown in FIG. 6, the peaksreflect PLC carrier regions and the notches reflect non-PLC carrierregions. Based on known or empirical data on PLC carrier regions andnon-PLC carrier regions, a plurality of frequency regions can beselected for use in monitoring signals on the power line. In thisexample, the frequency hopping sequence can include five selectedfrequency regions f1, f2, f3, f4 and f5 to be monitored on the powerline. The frequency regions f1, f3 and f5 (e.g., notches) exclude noisesuch as PLC carriers. The frequency regions f2 and f4 (e.g., carrierregions) include noise such as PLC carriers.

FIG. 7 illustrates a graph 700 of impedance versus frequency of a powerline communication network, showing frequency selection criteria basedon the network impedance in accordance with an example embodiment of thepresent disclosure. In this example, the graph 700 can reflect thenetwork impedance in a branch circuit, e.g., a kitchen wall outlet. Asshown in the graph 700, there are noisy ranges and quiet ranges thatcorrespond to certain aspects of the power line network. Frequencyregions can be selected from a preferred range to include a combinationof noisy regions and quiet regions in order to obtain a fuller pictureof signal events occurring on the power line given the wideband natureof signals produced by an arcing. It is expected that arcing can morereadily be seen on the quiet regions due to its wide band nature.

FIG. 8 illustrates a graph 800 of frequency versus time of an examplefrequency-hopping sequence of frequency regions for sampling signals ona power line in accordance with an example embodiment of the presentdisclosure. In this example, the frequency hopping sequence includes Mdifferent frequency regions (e.g., frequency steps 1, 2, . . . M), whichhave sequentially increasing frequencies. The frequency hopping sequenceis repeated N times over a predefined time period. However, it should beunderstood that the frequency hopping sequence can have a sequence offrequency regions that do not sequentially increase or decrease infrequency, such as shown in the graph 900 in the example of FIG. 9.

FIG. 10 illustrates a data stream 1000 of energy measurement samples,such as for example RSSI voltage samples, for a M-regionfrequency-hopping sequence. The sequence can be implemented N-times overa predefined time period, such as a half-cycle, to produce M×N energymeasurements. The energy measurement samples can be output from the ADC230 of FIGS. 2 and 3.

FIG. 11 illustrates an example M×N matrix of energy measurement samples,such as in FIG. 10, which is used to calculate an energy level for eachfrequency region in the frequency-hopping sequence in accordance with anexample embodiment of the present disclosure. As shown in FIG. 11, theM×N matrix includes samples of energy measurements for each of the Mfrequency regions (e.g., S₁₁ . . . S_(1N), . . . S_(M1) . . . S_(MN)).In this example, the energy measurement samples are RSSI samples thatform the matrix (e.g., RSSI space). The matrix can be used to computethe auto-correlating peak energy level, e.g., E_(m)=max(ACR_(m))=Σ_(i=1)^(N)(s_(mi)), for each of the M frequency regions, where m is the orderof the frequency region between 1 to a maximum M in a frequency hoppingsequence, n is a number from 1 to a maximum N that the frequency hoppingsequence is performed, M is the number of frequency steps, N is thenumber of sweeps within a half-cycle, and S is an energy measurementsample at a frequency step of a frequency hopping sequence.

As previously discussed, binary classification can then be performed foreach frequency region by comparing the energy level of the region to anenergy threshold. The threshold can be determined based on somestatistical analysis of different measurements performed in a controlledlaboratory environment.

FIG. 12 illustrates a voting strategy 1200, which is shown in a tableformat, for determining a presence or absence of an arc fault eventaccording to the calculated energy levels for each region of thefrequency-hopping sequence in accordance with an example embodiment ofthe present disclosure. In this example, there are five frequencyregions (e.g., M=5) that are monitored using the frequency hoppingsequence. The five frequency regions include 2 noisy bands (e.g., withnoise such as PLC carrier bands) and 3 quiet bands (e.g., without noisesuch as PLC carrier bands). An arc fault event (ARC) is detected when apredefined condition is satisfied, e.g., four or more frequency regions(or a combination of specific regions) have energy levels reflecting apresence of signal content, as shown in the table. The voting strategytable is provided as one example of a predefined condition. Othercombinations of the frequency region/energy level, such as for examplethose combinations of noisy and quiet bands on the table which areneither identified as ARC or No ARC, can also reflect an arcingsignature, and thus, an arc fault event.

It should also be understood that the example embodiments disclosed andtaught herein are susceptible to numerous and various modifications andalternative forms. Thus, the use of a singular term, such as, but notlimited to, “a” and the like, is not intended as limiting of the numberof items. Furthermore, the naming conventions for the variouscomponents, functions, thresholds, masks and other elements used hereinare provided as examples, and can be given a different name or label.

It will be appreciated that the development of an actual, realcommercial application incorporating aspects of the disclosedembodiments will require many implementation specific decisions toachieve the developer's ultimate goal for the commercial embodiment.Such implementation specific decisions may include, and likely are notlimited to, compliance with system related, business related, governmentrelated and other constraints, which may vary by specificimplementation, location and from time to time. While a developer'sefforts might be complex and time consuming in an absolute sense, suchefforts would nevertheless be a routine undertaking for those of skillin this art having the benefit of this disclosure.

Using the description provided herein, the example embodiments may beimplemented as a machine, process, or article of manufacture by usingstandard programming and/or engineering techniques to produceprogramming software, firmware, hardware or any combination thereof.

Any resulting program(s), having computer-readable program code, may beembodied on one or more computer-usable media such as resident memorydevices, smart cards or other removable memory devices, or transmittingdevices, thereby making a computer program product or article ofmanufacture according to the embodiments. As such, the terms “article ofmanufacture” and “computer program product” as used herein are intendedto encompass a computer program that exists permanently or temporarilyon any computer-usable medium or in any transmitting medium whichtransmits such a program.

A processor(s) or controller(s) as described herein can be a processingsystem, which can include one or more processors, such as CPU, GPU,controller, FPGA (Field Programmable Gate Array), ASIC(Application-Specific Integrated Circuit) or other dedicated circuitryor other processing unit, which controls the operations of the devicesor systems, described herein. Memory/storage devices can include, butare not limited to, disks, solid state drives, optical disks, removablememory devices such as smart cards, SIMs, WIMs, semiconductor memoriessuch as RAM, ROM, PROMS, etc. Transmitting mediums or communicationmediums or networks include, but are not limited to, transmission viawireless communication (e.g., Radio Frequency (RF) communication,Bluetooth®, Wi-Fi, Li-Fi, etc.), the Internet, intranets,telephone/modem-based network communication, hard-wired/cabledcommunication network, satellite communication, and other stationary ormobile network systems/communication links.

Furthermore, the arc fault detection features and functions, describedherein, can be implemented in a circuit breaker, or across separatecomponent(s) or module(s), which can communicate and interact with acircuit breaker or other power interruption device to facilitateinterruption of power (e.g., current or voltage) on a power line of acircuit when an arc fault event is detected. For example, the signalsample processing performed over a predefined period (e.g., ahalf-cycle), as described herein, can be implemented in the sameprocessor or controller, or a separate processor (e.g., a separate ASICor FPGA which can also include the components of the analog front end).

In addition, the predefined time period can be a half-cycle of a basefrequency, a full-cycle of a base frequency or any number ofhalf-cycles. The number M of frequency regions in the frequency hoppingsequence, and N repetitions of the sequence can be selected to obtain asuitable amount of energy measurement samples within a selectedpredefined time period, or vice-a-versa.

While particular embodiments and applications of the present disclosurehave been illustrated and described, it is to be understood that thepresent disclosure is not limited to the precise construction andcompositions disclosed herein and that various modifications, changes,and variations can be apparent from the foregoing descriptions withoutdeparting from the invention as defined in the appended claims.

The invention claimed is:
 1. A method of detecting an arc fault on apower line, comprising: repeatedly sampling a high frequency signal on apower line sequentially at different frequency regions according to afrequency hopping sequence over a predefined time period, the differentfrequency regions including at least one frequency region that includesa carrier for power line communication on the power line and at leastone frequency region that excludes a carrier for power linecommunication on the power line; computing a plurality of energy levelsfor the frequency regions of the frequency-hopping sequence, based on aplurality of energy measurements of the sampled high frequency signals;classifying the frequency regions in the frequency hopping sequence ashaving a presence or an absence of signal content in the respectivefrequency region, according to the computed energy level correspondingto the respective frequency region; and determining a presence orabsence of an arc fault event based on the classifications of thefrequency regions.
 2. The method of claim 1, wherein a frequency of eachfrequency region sequentially increases or decreases in the frequencyhopping sequence.
 3. The method of claim 1, wherein the obtaining anenergy measurement comprises: for each iteration of the frequencyhopping sequence, generating an energy envelope or received signalstrength indicator (RSSI) voltage sample for each frequency region inthe frequency hopping sequence based on the sampled high frequencysignal.
 4. The method of claim 3, wherein the computing an energy levelcomprises: for each frequency region, auto-correlating the plurality ofenergy envelopes or RSSI voltage samples of the frequency region toobtain a peak energy value as the energy level, or summing squared RSSIvoltage samples of the frequency region to obtain a summed energy valueas the energy level.
 5. The method of claim 1, wherein the frequencyhopping sequence includes a sequence of M frequency regions, and thefrequency hopping sequence is performed N times, the computing computesthe energy level for each of the M frequency regions using the followingequation:E _(m)=max(ACR_(m))=Σ_(n=1) ^(N)(s _(mn)), where: m is the orderfrequency region between 1 to a maximum M in the frequency hoppingsequence, n is a number from 1 to a maximum N that the frequency hoppingsequence is performed, S is an energy measurement sample at a frequencystep of a frequency hopping sequence, E_(m) is an energy level for afrequency hopping sequence m, and max(ACR_(m)) is a peak autocorrelationof N-energy measurement samples for a frequency hopping sequence m. 6.The method of claim 1, wherein the sampling a high frequency signalcomprises: for each frequency region in the frequency-hopping sequence,down converting the high frequency signal associated with the frequencyregion, applying a low pass filter to the down converted signal, andgenerating an energy envelope or RSSI sample for the filtered signal. 7.The method of claim 1, wherein the determining a presence or absence ofan arc fault event further comprises determining whether theclassifications of the frequency regions in the frequency hoppingsequence satisfy a predefined condition.
 8. The method of claim 1,wherein the predefined time period is a half-cycle of a base frequency.9. The method of claim 1, further comprising: causing interruption ofpower on the power line when an arc fault event is detected.
 10. An arcfault detection device for detecting an arc fault on a power line,comprising: an analog front end configured to: repeatedly sampling ahigh frequency signal on the power line sequentially at differentfrequency regions according to a frequency hopping sequence over apredefined time period, the different frequency regions including atleast one frequency region that includes a carrier for power linecommunication on the power line and at least one frequency region thatexcludes a carrier for power line communication on the power line; amemory; and one or more processors, in communication with the memory,configured to: compute a plurality of energy levels for the frequencyregions of the frequency-hopping sequence, based on a plurality ofenergy measurements of the sampled high frequency signals; classify thefrequency regions in the frequency hopping sequence as having a presenceor an absence of signal content in the respective frequency region,according to the computed energy level corresponding to the respectivefrequency region; and determine a presence or absence of an arc faultevent based on the classifications of the frequency regions.
 11. Thedevice of claim 10, wherein a frequency of each frequency regionsequentially increases or decreases in the frequency hopping sequence.12. The device of claim 10, wherein, to obtain an energy measurement,the analog front end is configured to: for each iteration of thefrequency hopping sequence, generate an energy envelope or receivedsignal strength indicator (RSSI) voltage sample for each frequencyregion in the frequency hopping sequence based on the sampled highfrequency signal.
 13. The device of claim 12, wherein, to compute anenergy level, the processor is configured to: for each frequency region,auto-correlate the plurality of energy envelopes or RSSI voltage samplesof the frequency region to obtain a peak energy value as the energylevel, or sum squared RSSI voltage samples of the frequency region toobtain a summed energy value as the energy level.
 14. The device ofclaim 10, wherein the frequency hopping sequence includes a sequence ofM frequency regions, and the frequency hopping sequence is performed Ntimes, the processor being configured to compute the energy level foreach of the M frequency regions using the following equation:E _(m)=max(ACR_(m))=E _(n=1) ^(N)(s _(mn)), where: m is the orderfrequency region between 1 to a maximum M in the frequency hoppingsequence, n is a number from 1 to a maximum N that the frequency hoppingsequence is performed, S is an energy measurement sample at a frequencystep of a frequency hopping sequence, E_(m) is an energy level for afrequency hopping sequence m, and max(ACR_(m)) is a peak autocorrelationof N-energy measurement samples for a frequency hopping sequence m. 15.The device of claim 10, wherein to sample the high frequency signal, theanalog front end is configured to: for each frequency region in thefrequency-hopping sequence, down convert the high frequency signalassociated with the frequency region, apply a low pass filter to thedown converted signal, and generate an energy envelope or RSSI samplefor the filtered signal.
 16. The device of claim 10, wherein theprocessor is configured to determine a presence or absence of an arcfault event when the binary values satisfy a predefined condition. 17.The device of claim 10, wherein the predefined time period is ahalf-cycle of a base frequency.
 18. The device of claim 10, wherein theanalog front end comprises: a mixer configured to sequentiallydemodulate the high frequency signal at different frequency regionsaccording to the frequency hopping sequence using a local oscillator orphase locked loop, the high frequency signal being demodulated by themixer to a baseband signal; and one or more band pass filters to filterthe high frequency signal or the demodulated baseband signal.
 19. Thedevice of claim 10, wherein the processor is further configured to causeinterruption of power on the power line when an arc fault event isdetected.
 20. A non-transitory tangible computer medium storing computerexecutable code, which when executed, is configured to implement amethod of detecting an arc fault on a power line, the method comprising:repeatedly sampling a high frequency signal on a power line sequentiallyat different frequency regions according to a frequency hopping sequenceover a predefined time period, the different frequency regions includingat least one frequency region that includes a carrier for power linecommunication on the power line and at least one frequency region thatexcludes a carrier for power line communication on the power line;computing a plurality of energy levels for the frequency regions of thefrequency-hopping sequence, based on a plurality of energy measurementsof the sampled high frequency signals; classifying the frequency regionsin the frequency hopping sequence as having a presence or an absence ofsignal content in the respective frequency region, according to thecomputed energy level corresponding to the respective frequency region;and determining a presence or absence of an arc fault event based on theclassifications of the frequency regions.